New study suggests low BMI is not an Alzheimer’s risk factor

Posted on 9th May 2017

The Journal of Clinical Endocrinology & Metabolism: Body Mass Index and Risk of Alzheimer Disease: a Mendelian Randomization Study of 399,536 Individuals

Researchers from Denmark have investigated the previously reported link between low body mass index (BMI) and Alzheimer’s disease, finding that the association is not causal. The study is published today in The Journal of Clinical Endocrinology & Metabolism.

The team studied people who are part of the Copenhagen General Population Study, randomly selecting participants so that the study population reflected the adult general population of people aged 20-100+ years. They included 95,578 people in the study, and these people had completed a questionnaire, physical examination and donated blood samples that were used for genetic analysis. The participants body weight and BMI was tracked by the researchers, beginning in 2003 and lasting for an average of seven years. None of the participants had a diagnosis of dementia at the start of the study, but the researchers used hospital records to calculate the number of people diagnosed with Alzheimer’s disease during the follow up period.

The researchers identified five versions of different genes that are strongly associated with BMI, and looked at the links between these genes, BMI and whether people developed Alzheimer’s.

Over the course of the study, 645 people were diagnosed with Alzheimer’s. The researchers found that the lower the BMI, the higher the risk of Alzheimer’s. However, when they accounted for the genetic analyses, they found that having a lower BMI was not linked with an increased risk of Alzheimer’s. The researchers concluded that lifelong low BMI due to genetic variation in BMI-related genes is not associated with an increased risk of Alzheimer’s.

Dr Rosa Sancho, Head of Research at Alzheimer’s Research UK, said:

“When links are found between two factors, such as BMI and Alzheimer’s risk, it is important to look behind that observation to try to understand which causes which. This new study has done just that, showing that people who are genetically predisposed to having a lower BMI are not at an increased risk of developing Alzheimer’s. The study suggests that people in the early stages of Alzheimer’s may experience weight loss, and that this could explain why researchers see a link between low BMI and increased Alzheimer’s risk.

“While there are currently no sure-fire ways to prevent dementia, current best evidence suggests that maintaining a healthy weight is a key way to keep our brains healthy. We also know that what is good for the heart is good for the brain, and that eating a healthy, balanced diet, exercising regularly, not smoking, and keeping blood pressure in check are all ways that help to reduce our risk of developing dementia.”

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